The invention relates to a method according to the preamble of appended claim 1 and a system according to the preamble of appended claim 9 for routing traffic in a node of a telecommunication network. The solution according to the invention is intended to be used especially in an exchange for routing calls made by users of a telephone network towards a desired subscriber (the called subscriber).
When a subscriber of a telephone network makes a call, the destination assigned for the call is determined in the exchange in accordance with the numbers selected by the subscriber. Each node of the telephone network finds out the destination of the incoming call by analyzing the selected numbers. In order that each node could forward calls, given information is transmitted relating to each call attempt, which information will in the following be referred to as call attempt data. The call attempt data includes e.g. the calling address, the called address and information on what kind of transfer media is required by the call in question.
The same destination can generally be reached along several alternative paths. A set of alternative paths typically correspond to a given destination in a transit exchange. Until an exchange can start operating, its routing functions must be established: routes are to be created, routes are to be grouped into destinations and digit analyses are to be created for providing the desired destinations as results.
Although the destination can be reached by using several alternative paths, some of the paths are shorter than the others. As it is preferable to route calls along the shortest (direct) route, routing is often carried out in such a manner that direct alternatives are tested first.
Routing functions typically carried out in an exchange are illustrated in FIG. 1 in a somewhat clarified way. The routing principle is hierarchical in such a manner that origin and digit analyses are carried out at the beginning on the basis of information on the calling subscriber and the selected numbers. The origin analysis is carried out to find out the information relating to the origin of the call. The information concerning the subscriber may be e.g. the origin of the incoming route (or circuit) and the subscriber class of the calling subscriber. Thus the same selected digit series received from different incoming circuit groups or from subscribers belonging to different classes may lead to a different result. The destination is obtained as a result of the analyses conducted. For example, there may be 65,000 destinations in the Applicant's DX 200 exchange each of which can contain 5 subdestinations. Subdestinations are typically divided into three main classes: connections directed to another exchange, subscriber lines in the same exchange and service triggers that initiate some service. A service of this kind can be of a very simple type, e.g a voice message delivered to the subscriber or a more complicated service that requires a conversation with a more remotely situated database (such as the service control point SCP in an intelligent network or the HLR register in the GSM network).
The destination also includes a so-called charging index which is supplied to the charging analysis (not shown in the figure).
One destination typically contains information on several, e.g. five different subdestinations. The subdestinations can be arranged within the destination into a given priority order in such a manner that one of them is the main alternative for routing. If e.g. a congestion is detected on the first subdestination, the call can be transferred to some other subdestination.
Each subdestination is further connected to one outgoing or internal route. The circuit groups associated with the desired route are tested after this in a given order to find an idle circuit. At this context a circuit refers to a combination of two transmission channels which enables a bidirectional transmission of signals between subscribers. A circuit group refers to a set of circuits with a similar purpose of use. The circuits of the circuit group have similar signalling properties.
The present invention relates to a routing hierarchy as described above and especially to the selection functions with which an alternative is selected from among many possible alternatives, such as the selection of a subdestination from among several alternative subdestinations in a destination.
When a call arrives at an exchange, the exchange generates a copy of the call control program and supplies it to be used by said call. The call control program calls routing functions. The call control attends to the call until it is terminated, whereby the copy is destroyed.
FIG. 2a illustrates these functions and in what way digit analysis and subdestination search is part of the processing of a call. A call control block CC supplies control information (containing e.g. said number and information with which analysis tree the digit analysis is to be carried out) to a digit analysis block DA that returns to the call control block information on the destination corresponding to the selected numbers. The destination refers at this context to a set of traffic control alternatives (i.e. subdestinations) that have been found on the basis of the digit analysis and other information, such as the subscriber class and the incoming circuit group. The call control block will forward these alternatives to the route selector RS that carries out an analysis of its own and returns the result to the call control block CC. This result is the subdestination mentioned above. The selection process employs data associated with a call attempt which data is known to the call control block CC. As digit analysis is not relevant to the present invention and as it can be carried out in a manner known per se, it will not be described in more detail herein. Digit analysis is described in more detail e.g. in Finnish Patent Application FI-943060.
An exchange is an expensive portion of a network and its useful life can generally be measured in decades. In the course of such a long time it may become necessary for various reasons to change the operation of the exchange. The needs for change may come from two different directions for the routing functions of an exchange:
1. The increase in the number of network services causes needs for change. As the number of services increases, there will also be an increase in the number of the parameters which have to be checked in connection with routing and which will have an effect on the result of routing.
2. Expenses are saved by dynamic routing methods that automatically adapt routing to the network mode. The use of such methods requires changes in the routing functions.
It is, however, quite difficult to change routing methods as the changes will have an effect on many different parts in the whole process. Therefore it will take quite a long while until the operator will obtain the desired changes from the manufacturer of the exchange.